Hi hazegry
Sorry I'm a bit late to the party, better late than never I guess. I built a sister ship by Latina "Marina II". Like you I decided to make an R/C version, not too difficult to do ... however, watch out, she is very top-heavy, make sure everything is as low in the hull as possible, and when you come to the trials ... keep her in shallow waters. I have mine sitting well below the waterline, and she still rolls perilously close to the point of capsizing. Oh, and DON"T over-power her.
The placing of the batteries is very limited - the forward end of the hold beneath the cabin structure, where, if your model kit is anything like mine, there is a deck installed above the inner wall of the hull; my advise would be to eliminate the deck; however, given that this thread is nearly six months old ... you're probably long past that point
Must be honest, mine usually stays on the shelf these days, as it's just too expensive replacing the electrical gear every time she wants to play shipwreck!